LIFE ON THE PLANETS. 813 



those influences and radiations which go to place upon their sur- 

 face the generative elements of life. Yet while these stars present 

 so strict analogies in formation and nature, they do not by any 

 means indicate the same degree of advancement in what may be 

 called geological or rather planetary evolution, or that which 

 tends to the appearance and development of life on their surface. 

 Here the conditions of mass, of distance from the sun, and doubt- 

 less other circumstances still unknown, come in to order the 

 epoch and the extent of these developments ; but we can affirm, 

 without going beyond the inductions permitted by the condition 

 of science, that if life has not yet been established directly on the 

 surface of any of the planets, we have very strong reasons for as- 

 suming its existence on some of them. We may regard this con- 

 clusion as gained from the long labors of antiquity and modern 

 discoveries. 



We say that, while the problem has not been directly re- 

 solved by the eyes, it has been worked out by an aggregate of 

 facts, analogies, and rigorous deductions that leave no room for 

 doubt. This is the mature and perfect fruit of science. It is the 

 view of intelligence, as certain an authority and of even a higher 

 and nobler order than the senses. I say further that what we 

 know of the unity of the chemical composition of the matter of 

 the sun, the stars, and the nebulae permits us to make new induc- 

 tions respecting the part performed by the bodies which are on 

 the earth the most important factors of the phenomena of life. 

 It is thus infinitely probable that hydrogen, oxygen, nitrogen, 

 carbon, and especially water, which on the earth are the indis- 

 pensable constituents of vegetable and animal life, fill a like 

 office not only in the planets of our system, but throughout the 

 universe. 



Water in particular, by virtue of its chemical functions and 

 the properties with which it is endowed in the solid, liquid, and 

 gaseous states properties which are so admirably fit for the ac- 

 complishment of physiological processes is a unique substance, 

 and the search through the whole series of chemical compounds 

 for any body that can take its place has been in vain. The dis- 

 covery of the spectrum of the vapor of water permits us to deduce 

 and assert its presence in the atmospheres of the planets and in 

 those of a whole class of stars as well. Drawing from these 

 results the fact of the presence of hydrogen, one of the generative 

 gases of water, in nearly all the stars, we are justified in supposing 

 an extreme diffusion of that important element from the point 

 of view of the unity of the phenomena which control the produc- 

 tion and maintenance of life. 



Thus, the more science advances, the more is that great law 

 confirmed and established of unity in the material elements, in 



